There is limited knowledge about the mechanisms by which GABAA receptors and other postsynaptic molecules concentrate at GABAergic synapses. GABAergic synapses are mostly inhibitory and play a major role in brain function. The long-term objective of this proposal is to identify the mechanisms involved in the postsynaptic clustering and anchoring of GABAA receptors and other postsynaptic molecules at GABAergic synapses. This proposal aims to 1) study the role of collybistin and gephyrin in regulating postsynaptic GABAA receptor clustering; 2) to study the role of protocadherin cell adhesion molecules in GABAergic synapses and 3) to study the role that a newly identified GABAA receptor-interacting protein plays in the clustering of the postsynaptic GABAA receptors. Light microscopy and electron microscopy immunocytochemistry with specific antibodies will be used for revealing the synaptic localization and clustering of GABAA receptors and postsynaptic proteins in the intact brain and in hippocampal cultures. Techniques such as RNAi and the expression of tagged postsynaptic proteins in cultured hippocampal neurons and in the intact brain will also be used. These studies are relevant for understanding the mechanisms involved in the synaptic targeting and postsynaptic clustering of GABAA receptors and GABAergic synaptic plasticity. It is predicted that the inappropriate postsynaptic clustering and localization of GABAA receptors would pathologically affect GABAergic synaptic function and brain development, leading to epilepsy and other neurological and mental disorders. PUBLIC HEALTH RELEVANCE: GABA is the main inhibitory neurotransmitter in the brain. The postsynaptic GABAA receptors and associated proteins play a fundamental role in the inhibitory synaptic transmission. Pathological alteration of GABAergic transmission has been linked to neurological and mental disorders including epilepsy, anxiety, depression, schizophrenia, autism and sleep disorders, among others. GABAA receptors are also the target of several therapeutic drugs used in the clinic and in anesthesia. Our proposed studies on the postsynaptic molecules involved in the clustering of GABAA receptors will be relevant for a better understanding of the mechanisms that control the assembly and normal function of GABAergic synapses and for designing strategies aimed to the amelioration of the diseases involving pathological alterations of these synapses.